The present invention generally relates to semiconductor devices and methods of producing semiconductor devices, and more particularly to a semiconductor device provided with a cap and a heatsink member and a method of producing such a semiconductor device.
Conventionally, a semiconductor element (flip-chip) having solder bumps or a semiconductor element having minute leads projecting to the periphery thereof is electrically coupled face downward to a multilevel interconnection layer (multilevel wiring layer) on a substrate and is fixed thereon. The semiconductor element is covered by a cap having the periphery thereof soldered on the top surface of the substrate, and the semiconductor element is hermetically sealed by the cap. A heatsink is fixed on the cap. The heat generated by the semiconductor element is conducted in a direction along the width of the cap and reaches the heatsink, and the heat is conducted within the heatsink and is radiated from the surface of the heatsink.
Generally, the cap is made of Kovar (registered trademark) when the coefficient of thermal expansion and the processing facility are considered. However, the thermal conductivity of Kovar is approximately 20 W/m.multidot.K and is unsatisfactory. For this reason, in a semiconductor device having the above-described construction, the cap acts as a resistance with respect to the thermal conduction and is an obstacle to the improvement of the heat radiating efficiency.
It is possible to conceive a construction in which the heatsink is mounted directly on the semiconductor element so as to improve the heat radiating efficiency, but in this case, it is difficult to obtain a perfect hermetic seal and to miniaturize the semiconductor device as a whole.
As another example of the conventional semiconductor device, there is a semiconductor device comprising a cap made of a material having a low thermal expansion coefficient for covering semiconductor elements. The cap has Cu embedded portions having a high thermal conductance. Such a semiconductor device is disclosed in IBM Technical Disclosure Bulletin, Vol. 26, No. 7A, December, 1983. According to this semiconductor device, a solid column made of high thermal conductance material is located on each semiconductor element and is in contact with the corresponding Cu embedded portion of the cap. The heat generated by the semiconductor element is conducted via the solid column and the Cu embedded portion of the cap. However, according to this semiconductor device, there is a problem in that the processes of producing the cap is complex since holes must be formed in the cap and the Cu embedded portions must be embedded in the holes. In addition, when the height of the semiconductor elements and the height of the solid column are inconsistent, a satisfactory contact may not be obtained between the semiconductor element and the solid column and between the solid column and the Cu embedded portion of the cap. However, when the cap is soldered on a substrate which has the semiconductor elements located thereon, it is virtually impossible to check whether or not the satisfactory contacts are obtained on the inside of the cap. Furthermore, since the solid column is located between the semiconductor element and the Cu embedded portion of the cap, it is impossible to reduce the height of the cap and the semiconductor device as a whole cannot be miniaturized.